斜日字布管螺旋折流板电加热器热力性能数值模拟

Numerical simulation on thermal performance of helical baffled electric heaters with one-plus-two U-tube units

斜日字布管三分螺旋折流板电加热器是针对现有分层环形布管弓形折流板电加热器存在的传热系数偏低和管间距不统一的缺陷而设计的一种正三角形布管的新型方案.对5种由27根16mm的U形管按斜日字布管的倾斜角为15°,20°三分螺旋折流板电加热器和2种由30根16 mm的U形管分层环形布管不同板间距的弓形折流板方案进行了流动与传热性能及表面温度均匀性的数值模拟和对比.流体为压缩氮气的计算结果表明:与性能相对较高的板间距200 mm弓形折流板方案相比,有效加热面积仅为68.5%的15°三分螺旋折流板电加热器的表面平均温度、最高温度分别降低了31.7,50.7 K,平均换热系数和综合指标h·Δp-1/3分别提高了68.2%,34.3%.

To overcome the defects of low heat transfer coefficient and non-uniform tube spacing in conventional multi-ring-annular U-tube layouts of segment baffled electric heaters,the novel helical baffled electric heaters with one-plus-two U-tube units were designed with equilateral triangle tube layouts. Numerical simulation and comparison of the flow and heat transfer performance and the surface temperature uniformity were performed for five helical baffled electric heaters and two segment baffled ones. Each helical baffled scheme comprises of nine one-plus-two U-tube units with altogether 27 16mm U-tubes supported by trisection helical baffles with 15° or 20° inclined angle,and each segment baffled scheme comprises of 30 16 mm U-tubes of two-ring annular layout supported by segment baffle plates spanned either 200 mm or 300 mm. The calculation results with fluid of compressed nitrogen show that the average temperature and the highest temperature of heating surface of 15° trisection helical baffles are reduced respectively by 31. 7 K and 50. 7 K,and the average heat transfer coefficient and the comprehensive index h·Δp- 1 /3are increased respectively by 68. 2% and 34. 3% than those of segment baffle plate scheme. The effective heating area of 15° inclined angled trisection helical baffle electricheater is only 68. 5% of that of segment baffled one with baffle plate span of 200 mm.